A comparison of small-scale, pilot-scale and large-scale tests for predicting leaching behaviour of landfilled wastes

Landfills generate emissions over long periods, often longer than a lifetime. The longest lasting emission is leachate. In order to estimate the future requirements for leachate treatment, different kinds of leaching tests may be applied. In this paper, shaking leaching tests (SLT), landfill-simulator leaching tests and a field-cell leaching test performed with ash, municipal solid waste (MSW) and MSW+ash are evaluated. The tests are compared and the factors influencing leaching are identified and discussed. The factors are: liquid to solid (L/S) ratio, water withdrawal, recirculation rate, presence or absence of biological processes, size of particles, duration of experiment, temperature and pre-treatment of the waste. The presence of biological processes has the greatest impact on leaching and is the main reason why SLT is less useful for long-term predictions. The landfill simulator tests were found to be useful for several different kinds of predictions. However, they are not reliable for predicting the L/S required for reaching a certain concentration. The possibilities for reliable long-term predictions would be facilitated by a better knowledge of the influence of various factors on leaching. Such an increased knowledge would make it possible to enhance waste stabilisation in leaching tests as well as in full-scale landfills.